Abstract
Bovine tuberculosis is a chronic disease impacting both public health and the livestock industry. The interferon (IFN)-γ assay has been introduced as an ancillary test for diagnosing bovine tuberculosis to overcome limitations of the skin test. The objective of this study was to assess the IFN-γ assay in terms of diagnostics and as a nationwide surveillance program in South Korea. From 2012 to 2013, cattle (n = 120) with bovine tuberculosis and cattle (n = 426) from bovine tuberculosis free herds were subjected to the IFN-γ assay to evaluate the sensitivity and specificity of the assay, respectively, depending on various cut-offs (0–3.5). When optical density of the cut-off was 0.1, the sensitivity and specificity were found to be 81.7% (74.7–88.6) and 99.5% (98.9–100.0), respectively. After introducing the IFN-γ assay as part of the national control program, the IFN-γ assay and single caudal fold skin test data were collected from 47 regional veterinary services to compare the results of these two tests. Overall, the agreement between the IFN-γ assay and the single caudal fold skin test (n = 492,068) was 98.2%, and Cohen's kappa value for the two methods was 0.47. Serial and parallel use of the IFN-γ assay and skin test for the bovine tuberculosis control program were compared using samples (n = 91) from cattle confirmed as bovine tuberculosis positive in laboratories from 2014 to 2016. Parallel screening for bTB showed much higher sensitivity (86/91, 94.5%) than the following screening approaches: serial (47.2%, 43/91), single screening using CFT (63.7%, 58/91), or the IFN-γ assay (78.0%, 71/91). These results indicate that the IFN-γ assay and single caudal fold skin test are complementary to each other; therefore, parallel use of these two tests is considered a useful approach to reduce the prevalence of bovine tuberculosis in South Korea.
Highlights
We attempted to assess the efficacy of the IFN-γ assay as a diagnostic tool and large-scale surveillance program for detection of bTB in South Korea
The calculation formula for the IFN-γ assay is based on the difference between the titers of IFN-γ that exist in each sensitized plasma sample using three kinds of stimulating materials, including bovine PPD, avian PPD, and PBS (O.DPPD−B-O.DPPD−A, O.DPPD−B-O.DPBS, O.DPPD−B > O.DPPD−A or O.DPPD−B-O.DPPD−A / O.DpositivecontrolO.Dnegativecontrol)
This calculation using PPDs accounts for sensitization by non-tuberculous organisms such as M. avium and IFN-γ in blood released for other reasons [6]
Summary
Interferon-γ Assay in the National Bovine Tuberculosis Control Program in South Korea. The interferon (IFN)-γ assay has been introduced as an ancillary test for diagnosing bovine tuberculosis to overcome limitations of the skin test. After introducing the IFN-γ assay as part of the national control program, the IFN-γ assay and single caudal fold skin test data were collected from 47 regional veterinary services to compare the results of these two tests. Parallel screening for bTB showed much higher sensitivity (86/91, 94.5%) than the following screening approaches: serial (47.2%, 43/91), single screening using CFT (63.7%, 58/91), or the IFN-γ assay (78.0%, 71/91) These results indicate that the IFN-γ assay and single caudal fold skin test are complementary to each other; parallel use of these two tests is considered a useful approach to reduce the prevalence of bovine tuberculosis in South Korea. Of the total tested cattle, results from 492,068 cattle that were tested concurrently using these two methods were analyzed for agreement using Cohen’s Kappa value [16]
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